So, theories we'ved spitballed about this are:
1) Canon is fully '70-200'-ing their 24-70 lenses into a lineup of (eventually) four offerings.
2) This is tailored for video -- STM, parfocal, etc.
3) It will be very small / very light in comparison to prior 24-70 lenses.
4) This is a 'value L' in the vein of 17-40, 70-200 F/4 non-IS. Cheap L glass for everyone.
I'll offer a fifth -- perhaps these new 24-70s are just a leap above in resolution for the impending high MP body? One would think the new 24-70 F/2.8 performance would speak to this, but I've seen:
- One stellar review (from Roger Cicala)
- One 'I got one good copy and one bad copy' from The Digital Picture
- One so-so review (from Photozone) on the resolution front.
So I'm not certain about this theory.
But golly gee, the speculation is awfully fun. Nothing like a CR3 to bring the band back together.